The 127 mm (5")/54 caliber (Mk 45) lightweight gun is a U.S. naval artillery gun mount consisting of a L54 Mark 19 gun on the Mark 45 mount. It was designed and built by United Defense, a company later acquired by BAE Systems Land & Armaments, which continued manufacture.
The latest 62-calibre-long version consists of a longer-barrel L62 Mark 36 gun fitted on the same Mark 45 mount. The gun is designed for use against surface warships, anti-aircraft and shore bombardment to support amphibious operations. The gun mount features an automatic loader with a capacity of 20 rounds. These can be fired under full automatic control, taking a little over a minute to exhaust those rounds at maximum fire rate. For sustained use, the gun mount would be occupied by a six-person crew (gun captain, panel operator, and four ammunition loaders) below deck to keep the gun continuously supplied with ammunition.
History
Development started in the 1960s as a replacement for the 127 mm (5")/54 caliber Mark 42 gun system that had debuted in 1953 with a new, lighter, and easier-to-maintain gun mounting. The United States Navy uses the Mark 45 with either the Mk 86 Gun Fire Control System or the Mk 34 Gun Weapon System. Since before World War II, 127 mm (5 inches) has been the standard gun caliber for U.S. Naval ships. Its rate of fire is lower than the British gun, but it fires a heavier 127 mm (5-inch) shell which carries a larger burst charge that increases its effectiveness against aircraft.
Variants
Mod 0
Used mechanical fuze setter. Two-piece rifled construction, with replaceable liner
Mod 1
Electronic fuze setter replaces the mechanical one. Made with a unitary construction barrel, which has a life span approximately twice that of the Mark 42 gun.
Mod 2
Export version of Mod 1, but now used in the U.S. Navy
Mod 3
Mod 2 gun with a new control system; never put into production
Mod 4
Receives a longer 62-caliber barrel (versus Mod 1 and 2's 54 caliber) for more complete propellant combustion and higher velocity and thus more utility for land attack. Was designed to use the Mark 171 Extended Range Guided Munition (ERGM), which was canceled. The Mk 45 mod 4 uses a modified flat-panel gun turret, designed to reduce its radar signature.
In sustained firing operations (Mode III), the gun is operated by a six-person crew: a gun captain, a panel operator, and four ammunition loaders, all located below decks. In fully automatic non-sustained firing operations (Mode IV), 20 rounds can be fired without any personnel inside the mount, using an automatic loader.
Ammunition
Mark 68 HE-CVT
Weight - 68.5 lb (31.1 kg) Projectile Length - 26.1 in (66.3 cm) Used only with Mods 0–2
Mark 80 HE-PD
Weight - 67.6 lb (30.7 kg) Projectile Length - 26 in (66 cm)
Mark 91 Illum-MT
Weight - 63.9 lb (29.0 kg) Projectile Length - 26.1 in (66.3 cm)
Mark 116 HE-VT
Weight - 69.7 lb (31.6 kg) Projectile Length - 26 in (66 cm)
Mark 127 HE-CVT
Weight - 68.6 lb (31.1 kg) Projectile Length - 26 in (66 cm)
Mark 156 HE-IR
Weight - 69.0 lb (31.3 kg) Projectile Length - 26 in (66 cm)
Mark 172 HE-ICM (Cargo Round) Projectile Length - 26 in (66 cm) Used only with Mod 4
Guided shell
On 9 May 2014, the U.S. Navy released a request for information (RFI) for a guided 127 mm (5-inch) round that could be fired from Mark 45 guns on Navy destroyers and cruisers. The thinking is that if the technology worked in the Long Range Land Attack Projectile (LRLAP) for the Advanced Gun System on s, it can be applied to a 127 mm (5-inch) mount. This RFI comes six years after the cancelation of the Raytheon Extended Range Guided Munition. The shell must have at least double the range of unguided shells for missions including Naval Surface Fire Support (NSFS)/Land Attack, and increasing anti-surface warfare (ASuW) capabilities against fast attack craft (FAC) and fast inshore attack craft (FIAC); the main purpose is to destroy incoming small boats at a greater range with a proximity fuse airburst blast fragmentation warhead to spray shrapnel over swarms.
Expected submissions include the BAE Systems Multi Service–Standard Guided Projectile (MS-SGP), Raytheon Excalibur N5, and OTO Melara Vulcano guided long-range projectile.